The pieces were all fairly dynamic, either from the way they were constructed, e.g., the Mary Corse piece in this video
Mary Corse from richard ferrante on Vimeo.
or others which changed substantially as as you walked by. For example, in this piece by Robert Irwin
the "blending point" (where the band blended with the background) changed as you walked around it.
Very difficult pieces to photograph. I recommend the Art in America article and associated slideshow: